Passenger elevators are typically raised or lowered by a cable running over a pulley at the top of an elevator shaft. A counterweight that balances the weight of the elevator car plus an average number of passengers is disposed at one end of the cable while the elevator car is attached to the other end. The car and counterweight run up and down the shaft on guide rails. An electric motor drives the pulley to move the car, needing only enough power to raise the difference in weight between car and passengers and the counterweight. The car is held at a floor by a hoist brake associated with the electric motor. The brake is typically urged on by springs and released by a solenoid. Thus an absence of electrical power sets the brake.
Electrical power outages safely brake the car at its position in the shaft but this situation may leave passengers trapped inside the car until rescue personnel can open shaft doors and extend ladders or ropes down to the car top. This effort can often require the efforts of several people. If the power outage is due to a natural catastrophe such as an earthquake it may be a considerable time before a sufficient number of rescue personnel are available. Apparatus that would allow a single person to effect a controlled release of the hoist brake and subsequent movement of the car could facilitate the prompt rescue of such people.
Special purpose apparatus has been developed for a variety of purposes such as the manual release mechanism for a spring-applied parking brake of U.S. Pat. No. 4,279,332 and the rail splice clamp of U.S. Pat. No. 2,256,192. Other special purpose tools are shown in U.S. Pat. Nos. 2,504,345, 2,566,454, 2,591,210, and 2,706,613.